Quality Park Survivor Expanding Catalog Mailers are made with durable 14 lb DuPont Tyvek, which is strong enough to withstand the most grueling conditions. The material is puncture, tear and moisture resistant—virtually indestructible. Yet, it is still lightweight which can provide a savings on shipping costs. Envelopes expand up to 2" for bulkier items, like books, large contracts and more. These 10" x 13" white mailing envelopes feature an easy Flap-Stik closure which requires no moisture for a secure seal and a release strip for quick, easy opening. Whether your sending critical documents or re-selling items on an online marketplace, Survivor Catalog Mailers are an efficient, cost effective way to make sure your items get there intact. 25 per box. Tyvek is a trademark of DuPont used under license by LSC Communications US, LLC d\/b\/a TOPS Products.